1. Field of the Invention
The present invention deals with a device forming part of a shoe or being insertable into a shoe to generate heat without the use of external energy.
2. DESCRIPTION OF THE PRIOR ART
In the case of ski boots, in particular, it is known to install an electrical resistance heater in the inner sole, the heater being actuated by a battery. A device of this type has the disadvantage that the generation of heat is dependent on an external energy source which has to be replaced at regular intervals.
Heat-insulating insoles are also known which, although they more or less effectively prevent the undesirable escape of heat, are not designed to generate heat.
Published Australian patent application No. 27,666/84 disclosed an insole for shoes consisting of two plastic films welded together at their edges and defining a cavity filled with a fluid. The fluid was locally displaced by the rolling motion of the foot and was thus moved within the cavity. In order to prevent the fluid from being displaced from the rear to the front and vice versa by the direct route, baffles in the form of partitions were arranged within the cavity. This type of insole serves to absorb the impacts arising during walking and exerts a certain massage effect, but does not cause any evolution of heat to take place.
An insole of a similar type is shown in U.S. Pat. No. 3,871,117. This insole likewise evidences a cavity filled with a fluid with the cavity being subdivided by partitions into a large number of chambers. The cavity is connected in the region of the toes and in the region of the heel to a cooling system arranged in the footwear through which the fluid is forced out of the cavity during walking. In order to insure a directed flow from the toes to the heel and then through the cooling system, a system of valves is positioned within the cavity. In the case of this sole, specific measures are taken to prevent evolution of heat in the shoe.
U.S. Pat. No. 4,123,855 likewise discloses an insole of the type mentioned which consists of two films connected to one another along their edges and serving to confine a fluid-filled cavity. The cavity is likewise subdivided by baffles which are formed by partitions. These baffles prevent the fluid from being displaced from rear to front and vice versa by direct flow during walking. This construction contemplates an increased massage effect. The insole is further provided with a number of continuous ventilation apertures which extend transversely to the longitudinal dimension of the sole. The purpose of the ventilation aperture is to prevent warming of the foot so that this sole also provides means for counteracting the evolution of heat in the footwear.